The proposed research aims to study 1) the mechanisms by which an embryonic cell first becomes committed to differentiate into a particular cell type (e.g. a cartilage cell), 2) the influence of particular environmental factors (cell-cell interaction and cell- extracellular matrix interaction) on the process of differentiation, and 3) the possibility of coregulation of the synthesis of two specialized products (collagen and proteoglycan) made by the same cells. The experimental method makes use of cell cultures of undetermined chick and mouse embryo mesenchyme cells where several environmental factors, such as cartilage conditioned medium and other extracellular materials, can be used as tools to study regulatory steps in cartilage cell differentiation.